1. Field of the Invention
The present invention relates to an image reading apparatus for reading out images from a document.
2. Description of the Related Art
Some conventional document feeding devices are provided with a reading device or a read-out sensor such as a CIS (Contact Image Sensor) at a location facing a feeding path, along which documents are fed page by page, and the read-out sensor reads out images in the document without any interruption in the feed. In a document feeding device having such a read-out function, it is necessary to prevent contamination of an optical receiver of the read-out sensor as far as is possible. If contamination of the optical receiver occurs black or white streaks will appear in images that are read out.
In view of the foregoing, for example, one related art discloses a technique for preventing contamination of an optical receiver by providing a cleaning roller upstream of the reading device, which removes contamination from an image intensive area on a surface of the document before it reaches the reading device.
Other related arts disclose a technique for performing shading correction by providing a reference color member beneath a feeding path, and causing the read-out sensor to read the reference color when pages of a document to be read are not on the feeding path. While one of the related arts described above discloses use of a guide roller having a white reference surface as a reference color member, another related art described above discloses use of a roller member having a white outer surface, a rotation member having a polygonal cross-section and white outer surfaces, a rotatable white belt member, or a windable roller-like white member, for use as reference color members.
However, according to the technique disclosed in the related art described above, while it is possible to remove contamination attached to a surface of a document page before it reaches the reading device, it is not possible to prevent contaminants such as paper particles, toner scum, dirt and dust, all of which may be agitated by movement of the document, from becoming attaching to the reading device.
According to the techniques disclosed in other related arts, since the reference color member is provided beneath the feeding path, paper particles, toner scum, dirt and dusts may easily become attached to the reference color member as contaminants over time, thereby interfering with reading out of a proper reference color. The technique also involves a problem in that it requires various complicated processes to be carried out relating to the shading correction process; for example, when the read-out sensor reads the reference color, the white reference surface of the guide roller should be aligned at a position opposing the read-out sensor, or the white belt member should be rotated, or the roller-like white member should be wound so as to replace a tainted reference surface with a clean new reference surface.